The present invention relates to a method and apparatus for separating gaseous or vaporous substances having different molecular weights and/or different gas kinetically effective cross sections, particularly isotopes, in which the mixture to be separated is conducted, together with a lighter additive gas, through two slit-shaped nozzles in the form of jets which are directed toward one another so as to be mutually deflecting, the jets thus entering a separating chamber and the thus deflected jets being separated into partial streams of respectively different compositions by means of separating baffles and being discharged separately, the lines of flow of the mixture to be separated converging radially during introduction into the separating chamber.
The principle of the so-called separating nozzle method is disclosed in German Pat. No. 1,052,955 and is based on the spatial partial separation of a jet expanding from a nozzle-like opening into a low pressure chamber at subatmospheric pressure. German Pat. No. 1,096,875 discloses advantages that can be realized in the practice of this method by addition of a light additive gas with a mole excess to the mixture to be separated and by using, if required, at least two converging gas streams.
German Pat. No. 1,198,328 teaches that the separating properties of an arrangement can be improved by mechanically deflecting the jet leaving the nozzle on its path toward the separating baffle by means of a curved wall so as to make the curvature of the flow lines and the size of the angle of deflection greater than would be possible in the expanding jet. The curvature of the flow lines produces a centrifugal field as a result of which the partial stream formed in the vicinity of the wall is heavier than that formed at a greater distance from the wall. The curved deflecting wall, however, produces friction losses which may reduce the separating effect.
An explanation of the generic process is given in the KFK Report 2138 of March 1975 by Kernforschungszentrum Karlsruhe published by Gesellschaft fur Kernforschung mbH. In it, it is stated, inter alia, that with jet-jet systems of this type, there may appear two completely different flow configurations, i.e. the desired, mirror symmetrical jet-jet deflection changes, above certain "critical" parameters, and a configuration in which the jets slide one on top of the other at a small mutual angle, as described at pages 37 et seq. of the above-cited report. This sudden conversion of the flow configuration is associated with a sudden drop in separation.
It has been found, as explained at pages 40 et seq. of the above-cited report, that this flow instability is associated with the fact that the mixture, e.g. UF.sub.6, which has been accelerated by the lighter additive gas, retains, due to its high inertia, approximately its original direction of flow even after leaving the opening of the nozzles, i.e. after passing through the most constricted point of the facing nozzles. That is, the UF.sub.6 flow lines continue to converge in a radial pattern even after leaving the opening of the nozzles so that a sharply bundled, or concentrated, UF.sub.6 jet is produced. This bundling and thus this tendency of mutual deflection of oppositely directed jets is reinforced by an increase in the limitation angle from 18.degree. to 30.degree.. It was thus decided not to further increase this limitation angle.
Due to these instabilities it was impossible, during prior studies, to realize any technological or economic improvements compared to other prior art separating nozzle systems. This was the more regrettable since it had also been found in these studies that a jet-jet separating system tends to be less subject to annoying dust deposits than arrangements provided with a fixed deflection wall.